The invention relates to apparatus and process for the biological treatment of liquid wastes employing fluidized beds. In particular, it is directed to a process for removing organic carbon or biochemical oxygen demand from waste water, and in one form it also removes oxidized nitrogen from nitrified effluent.
Waste water treatment plants are typically designed to remove solids and oxygen demanding organic material. Traditionally, activated sludge or trickling filter processes were employed to accomplish the required treatment incorporating theuse of primary and final settling tanks for solids removal. Activated sludge treatment involves the use of microbial organisms to consume the organic wastes. The organisms are cultured as suspended solids in biologically active aeration tanks. Biological oxidation is accomplished primarily in the aeration tank where from 1000 to 4000 mg/l of highly active biological solids are typically maintained under aerobic conditions. Air is most often used to provide sufficient oxygen for the oxidative process as well as to keep the waste liquor well mixed with the suspended solids to prevent settling in the aeration tank. In conventional activated sludge treatment systems, about six hours of aeration time is required to provide satisfactory removal of the organic contaminants. Following the aeration step the waste liquor with the suspended solids are conveyed into the final setting tank where the supernatant liquor is separated from the suspended solids, the liquor is normally discharged as the final effluent, while the suspended solids are partially wasted and recycled to the aeration tank where they again consume organic waste.
Traditional trickling filter processes employ four to ten foot beds of 2 to 4 inch stone, upon which biological slimes grow. Liquid waste is intermittently applied over the stones, typically by a rotary distributor which revolves around the circular trickling filter bed of stones. As waste water trickles over the biological slimes covering the stones, the organic wastes are oxidized. Air which fills the voids of the stones provides the oxygen necessary for the biological oxidation.
Both the traditional activated sludge and trickling filter processes are costly and require much space and extensive building requirements. Construction costs of the two processes are fairly comparable in small sized plants, but activated sludge is often more economical for larger installations. In general, those processes provide a substantial reduction of the five-day biochemical oxygen demand (EOD).sub.5 and suspended solids present in, for example, municipal waste water. These processes, in effect, convert the organic contaminant, typically measured as BOD.sub.5, to innocuous carbon dioxide and water; but also produce biological mass which must be given further treatment. Such processes are highly expensive and require much land, personnel and lead time to design and construct to meet today's critical needs for waste water purification systems.
New activated sludge processes in the developmental stages use pure oxygen and suspended solids of 3,000 to 6,000 mg/l in the aeration tanks, but still require from 2 to 4 hours aeration time, as well as bulky tanks and piping systems.
In the past, experimenters have employed up-flow expanded beds containing activated carbon for the absorption of minor amounts of organic carbon (BOD) that remained after conventional biological treatment or physical/chemical treatment. Such absorption processes employing expanded beds were primarily experimental and not used for large scale waste water purification systems. Frequent back-washing or regeneration of the system was needed as the pores in the activated carbon tended to become rapidly filled with contaminants. Examples of such up-flow expanded bed type systems are described in the following publications: Weber, W. J. Jr., Hopkins, C. B. and Bloom, R. Jr. "Physiochemical Treatment of Waste Water", Journal of Water Pollution Control Federation, 42, 83-89 (1969); Weber, W. J. Jr., Hopkins, C. B. and Bloom R. Jr., "Expanded-Bed Active-Carbon Adsorption Systems for Waste Water Treatment", Gloyna and Eckenfelder, Ed. University of Texas Press, 1970; and in U.S. Pat. No. 3,658,697 issued Apr. 25, 1972. However, it will be particularly appreciated that the biochemical oxygen demand was primarily removed from the waste water by an adsorption process and not by a biological process. In addition, an up-flow expanded bed of activated carbon was employed as compared to a fluidized bed, as will be discussed more fully hereinafter.
Laboratory scale experimentation has been conducted using up-flow packed bed reactors operated under anaerobic conditions. These reactors used 1 to 1.5 inch stones as a media and required an 18 hour detention time to achieve 90 percent BOD removal.
While the art has recognized the desirability of employing biological organisms to remove organic carbon, it has not succeeded in providing an inexpensive and highly efficient process for rapidly treating large quantities of waste water. Accordingly, there exists a critical need for a process free of the defects and deficiencies of the prior art to purify waste water.
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______________________________________ Publications ______________________________________ Tamblyn, T. A. and Sword, Bryan R.; "The Anaerobic Filter for the Denitrification of Agricultural Subsurface Drainage" Paper presented at 24th Annual Purdue Industrial Waste Conference, Lafayette, Indiana on May 7, 1969. Beer, Carl, "Evaluation of Anaerobic Denitrification Processes", Proc. Paper 7211, Seidel, D. F. and Crites, R. W., Ed., (April, 1970). Castaldi, F. and Jeris, J. S., "Still Wanted: Economical Controlled Denitrification", Water and Wastes Engineering Vol. 41, 36-38 (June, 1971). Beer, C., Jeris, J.S. and Mueller, J. A. "Biological Denitrification of Effluents in a Fluidized Granular Bed, Phase I" prepared for N.Y. State Department of Environment Conservation, publ. Manhattan College; (March, 1972). Weber, W. J. Jr., and Morris, J. C. "Kinetics of Adsorption in Columns of Fluidized Media", Journal of American Water Works Association, pp. 425, 430, Vol. 443, (1965). St. Amant, P. P. and McCarty P. L., "Treatment of High Nitrate Waters", Journal of American Water Works Association pp. 659-662, (1969). McCarty, Perry L. and Haug, Roger T., "Nitrification with submerged Filters" Journal Water Pollution Con- trol Federation, Vol. 44, No. 11 (November, 1972). McCarty, Perry L. and Young, James C., "The Anaerobic Filter for Waste Treatment", Journal Water Pollution Control Federation, Vol. 41, R160 (1969). Weber, W. J., Jr., Friedman, L. D. and Bloom, R. Jr., "Biologically - Extended Physicoclogical Treatment", Paper presented at 6th International Water Pollution Control Conference at the University of Michigan on June 22, 1972. ______________________________________